For examples of tuning one- and two-degree-of-freedom PID compensators, see:- “PID Controller Tuning in Simulink”
- “Tune PID Controller to Favor Reference Tracking or Disturbance Rejection” on page
7-23
What Plant Does PID Tuner See?
PID Tuner considers as the plant all blocks in the loop between the PID Controller block
output and input. The blocks in your plant can include nonlinearities. Because automatic
tuning requires a linear model, PID Tuner computes a linearized approximation of the
plant in your model. This linearized model is an approximation to a nonlinear system,
which is valid in a small region around a given operating point of the system.By default, PID Tuner linearizes your plant using the initial conditions specified in your
Simulink model as the operating point. The linearized plant can be of any order and can
include any time delays. The PID tuner designs a controller for the linearized plant.In some circumstances, however, you want to design a PID controller for a different
operating point from the one defined by the model initial conditions. For example:- The Simulink model has not yet reached steady-state at the operating point specified
by the model initial conditions, and you want to design a controller for steady-state
operation. - You are designing multiple controllers for a gain-scheduling application and must
design each controller for a different operating point.
In such cases, change the operating point used by PID Tuner. See “Opening PID Tuner”
on page 7-6.For more information about linearization, see “Linearize Nonlinear Models” on page 2-3.PID Tuning Algorithm
Typical PID tuning objectives include:- Closed-loop stability — The closed-loop system output remains bounded for bounded
input. - Adequate performance — The closed-loop system tracks reference changes and
suppresses disturbances as rapidly as possible. The larger the loop bandwidth (the
7 PID Controller Tuning